Audio signal time offset refers to the delay introduced into an audio signal by a piece of audio equipment such as telephone equipment. Determining audio signal time offset is useful as audio time offsets occur in many different types of audio equipment. These time offsets are often important to those who use that equipment, but there is often no effective way to accurately measure these time offsets. Potential users of this algorithm include persons who design, build, test and use audio equipment. Examples include telephone, cellular telephone, personal communications, and satellite service providers, equipment manufacturers, and users. Further examples include those who make, install and use digital audio encoders and decoders.
Conventional techniques for measuring such delay may be hampered where the audio signal is distorted or otherwise altered by the audio equipment itself. It may be difficult to compare the input and output audio signals when the two signals are no longer identical due to distortion or alteration induced by the audio equipment.
In evaluating audio equipment, it may be useful to determine whether an output audio signal is perceived as identical or nearly identical to an input audio signal. Of course, it is a simple matter using electronic tools to determine whether an output audio signal is electronically identical to an input audio signal. However, in many applications, particularly telephony, it may be more useful to determine whether the average listener perceives an output audio signal to be identical or nearly identical to an input audio signal. An output audio signal may be perceived as being identical or nearly identical to an input audio signal even if significant distortion or alteration to the input audio signal takes place. Since, in application, perception is paramount, it may be possible to build audio equipment which introduces significant distortion without degradation of the perceived output audio signal.
Traditionally, measuring perception of an output audio signal was a time-consuming manual process. A number of audio signals may be played for a sampled cross-section of listeners, and each listener asked to evaluate each audio signal. The evaluations of each listener may be compiled and averaged, and each audio signal rated in terms of its perception. Such a technique, in addition to being time-consuming and costly, may also be inaccurate. For example, one must insure that the listeners sampled represent a cross-section of the spectrum of the hearing abilities of the average listener. Moreover, human variation in scoring such perceptional based evaluations may introduce additional error.
Heretofore, there has not been a technique for electronically evaluating an output signal to determine human perception in a consistent manner.